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California scientists have discovered a homegrown coronavirus strain that appears to be propagating faster than any other variant on the loose in the Golden State.

Two independent research groups said they stumbled upon the new strain while looking for signs that a highly transmissible variant from the United Kingdom had established itself here. Instead, they found a new branch of the virus’ family tree — one whose sudden rise and distinctive mutations have made it a prime suspect in California’s vicious holiday surge.

As they pored over genetic sequencing data in late December and early January, the two teams saw evidence of the new strain’s prolific spread leap off their spreadsheets. Though focused on different regions of the state, they uncovered trends that were both remarkably similar and deeply worrying.

Researchers at Cedars-Sinai Medical Center in Los Angeles found that although the strain had been barely detectable in early October, it accounted for 24% of roughly 4,500 viral samples gathered throughout California in the last weeks of 2020.

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